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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

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346

TABLE   XLI

Unit.
	Hefner Candle.
	International Candle, Decimal Candle (Normal Candle), American Candle, Pentane Candle.
	Carcel.

Hefner candle    ....
	I
	0-9
	0-093

International candle, decimal candle (normal candle, American candle, pentane candle .....
	I'll
	i
	O'lo^1:


	
	
	

Carcel           .....
	lO-?")
	9-6=;
	i


	
	
	

The petroleum to be tested is poured into a lamp and the latter weighed,
centred on the photometric bench and lighted, the time being noted. The
flame is kept low at first and is then gradually raised until it is as large as
possible without smoking and without the wick charring excessively. Photo-
metric observations are then begun and are repeated at regular intervals
—the time of each being noted—until the oil is almost exhausted, the wick
not being further moved; the lamp is finally extinguished and weighed,
the consumption of oil being thus ascertained.

The position of the Hefner lamp is taken as the zero of the scale and
that^of the oil lamp as 300 cm. ; the illuminating power of the lamp is then
given by the formula,

I/   —-—

where i is the intensity required, expressed in candles (Hefner), / the
length of the photometric bench and % the distance of the photometer
screen from the zero point of the scale. The mean of the different obser-
vations gives the mean intensity in candles.

The mean consumption per candle-hour is the quotient of the total
weight of oil used by the total candle-hours, and the yield, that is the
amount of light (in candle-hours) produced per gram of oil, the quotient
of the total candle-hours by the weight of oil consumed.

It is necessary also to take account of the variation of the luminous
intensity during the experiment. As a rule, after reaching its maximum
a few minutes subsequent to the lighting of the lamp, it diminishes more
or less slowly to the end, mainly on account of the carbon ring formed at
the summit of the wick in consequence of the incomplete combustion of
the heavier fractions, this hindering the rise of the oil into the flame. This
decrease is expressed by a fraction, the numerator of which is the difference
between the maximal luminous intensity reached soon after the beginning
and that observed just before the exhaustion of the oil, and the numerator
the maximal intensity.e